1. Field of the Invention
The present invention relates to a wireless transmission system, such as an analog cordless telephone system, wherein a main device and one or more auxiliary devices communicate with each other by wireless transmission using multiple access.
2. Description of the Related Art
Analog cordless telephone systems have recently become popular. An analog cordless telephone system includes a main device, which is connected to a telephone line, and a plurality of auxiliary devices.
Using multiple access technology, wherein the main device and the auxiliary device share a call channel to communicate with each other, a free call channel is selected from a plurality of call channels. An outgoing frequency of the free call channel is used for transmission from the main device to the auxiliary devices and an incoming frequency of the free call channel is used for transmission from the auxiliary devices to the main device. Full duplex mode is used to communicate frequency modulated (FM) audio signals of a telephone call over the pair of call channels between the main and auxiliary devices.
On the other hand, half duplex mode is normally used to communicate a variety of data between the main and auxiliary devices before the telephone call, by modulating the call channel in frame-length time slots using minimum shift keying (MSK). That is, when the main device receives an incoming call, the main device first calls all of the auxiliary devices in order over the selected transmission channel before the actual telephone call is connected. The auxiliary devices ring as a result. Once a user picks up one of the ringing auxiliary devices, that is, brings the auxiliary device into an off-hook situation, the auxiliary device transmits a response at this timing to the main device. Accordingly, the main device sends a connection command to the auxiliary device, and starts the telephone call using the auxiliary device.
However, when a great number of auxiliary devices are registered in the cordless telephone system, then a great deal of time is required for the main device to call all the auxiliary devices one at a time in order. For this reason, a great deal of time may elapse from when a auxiliary device goes into an off-hook situation, until the main device sends the connection command. For example, if the user picks up the auxiliary device, so that the auxiliary device goes into an off-hook condition immediately after the auxiliary device was called by the main device, then the user must wait for the main device to call all of the other auxiliary devices, one at a time in order, before the auxiliary device responds to the call, whereupon the main device issues a connection command, and the telephone call actually starts. The total time required for connection increases. The response time from when the phone is picked up until start of the telephone conversation is delayed, which makes the telephone system difficult to use.
It is an objective of the present invention to provide a wireless transmission system with a main device that calls a plurality of auxiliary devices over a call channel before a telephone call is started, wherein the system is capable of quickly starting telephone conversations even when the system includes a great number of auxiliary devices, and is capable of preventing signals from different devices from mixing when communication is performed using a multiple access scheme.
To achieve the above-described objectives, a wireless transmission system according to the present invention includes a main device and a plurality of auxiliary devices that communicate data therebetween using a multiple access transmission scheme. The main device transmits to the plurality of auxiliary devices over an outgoing frequency of a single wireless channel. The plurality of auxiliary devices transmit to the main device over an incoming frequency of the single wireless channel.
The main device and the plurality of auxiliary devices communicate in time slots that repeat in cycles. That is, each cycle includes first through third time slots. The first time slot is allotted for the main device to transmit a call signal to the plurality of auxiliary devices. The second time slot is allotted for at least one of the plurality of auxiliary devices to transmit a notification signal notifying that the single wireless channel is presently being used. The third time slot is allotted for any of the plurality of auxiliary devices to transmit a response signal requesting a response from the main device.
With this configuration, when a main device receives an incoming call, it transmits a call signal to the plurality of auxiliary devices using the first time slot. Also, in each cycle, one or more of the auxiliary devices transmit the notification signal using a second time slot. Further, when a auxiliary device is brought into an off-hook condition, it transmits a response signal to the main device in the third time slot.
All of the devices, that is, the main device and the auxiliary devices, transmit and receive information using the three time slots in a repeating cyclical configuration. As a result, even if the number of the auxiliary devices increases, each cycle will still only have a single second time slot and a single third time slot. Since the time required to contact all of the auxiliary devices does not increase, the time from when the main device calls the auxiliary devices until when the auxiliary device responds will remain short.
Because one or more of the auxiliary devices transmit the notification signal using a second time slot, the main device of other systems, for example other cordless telephone systems, can be notified that it should not attempt to use the wireless channel presently being used by the present system. Interference between transmissions of different systems can be prevented.
It is desirable that all of the plurality of auxiliary devices transmit the notification signal in the second time slot of each cycle, because the main device of other cordless telephone systems can be even more reliably notified that the particular wireless channel used by the present system is being used.
It is also desirable that the main device transmit the call signal with designation data that designates which of the auxiliary devices should transmit the notification signal. In this case it is desirable that each auxiliary device include a distinguishing unit that determines whether the designation data designates the corresponding auxiliary device or not. With this configuration, when the main device calls the plurality of auxiliary devices, the main device transmits a call signal to all of the auxiliary devices in a first time slot and, by using designation data included in the call signal, simultaneously designates the auxiliary device that should transmit the notification signal. Each auxiliary device that receives the call signal determines whether the designation data indicates itself, that is, the auxiliary device itself, or not. Accordingly, the most suitable auxiliary device, that is, according to the operating conditions of the auxiliary devices, can be flexibly designated for transmitting the notification signal.
It is also desirable that at least one of the plurality of auxiliary devices transmits the notification signal with distinguishing data that indicates which auxiliary device is transmitting the notification signal. In this case, it is desirable that the main device include a distinguishing unit that determines which auxiliary device is indicated by the distinguishing data.
With this configuration, the auxiliary device that should transmit the notification signal transmits distinguishing data in the notification signal in order to indicate itself as the device that is transmitting the notification signal. Upon receiving the notification signal, the main device determines which auxiliary device transmitted the notification signal based on the distinguishing data. Accordingly, the main device can determine whether the auxiliary device is properly transmitting the notification signal and also grasp the operating conditions of the auxiliary device.
It is desirable that one or more of the auxiliary devices transmit, in each second time slot, the notification signal in the form of an unmodulated carrier corresponding to the incoming frequency of the single wireless channel. With this configuration, the auxiliary device or devices that should send the notification signal transmits a non-modulated carrier having the incoming frequency. Accordingly, the auxiliary device or devices need not generate data or perform processes required for modulation, and so can quickly and easily transmit a notification signal.
It is desirable that the plurality of auxiliary devices each be set with a different retry number that indicates a number of consecutive cycles during which the corresponding auxiliary device should try to retransmit the response signal in the third time slot.
With this configuration, when the main device calls a plurality of auxiliary devices, any auxiliary device that requires a response transmits a response signal in the third time slot. If the auxiliary device does not receive permission to connect from the main device, then the auxiliary device again transmits the response signal in the third time slot. The auxiliary device repeatedly transmits the response signal until either a response is received from the main device or the auxiliary device sends the response signal in a number of consecutive cycles corresponding to the retry number.
Accordingly, even if two or more of the auxiliary devices start transmitting their response signals at the same timing, so that transmission of response signals collide, after one auxiliary device completes its predetermined number of retries, another auxiliary device will still be able to transmit a response signal. As a result, at least one of the auxiliary devices will be able to transmit a response signal so that the auxiliary device can quickly and reliably start telephone communication.
It is desirable that each auxiliary device includes a retry determination unit that determines, based on a predetermined probability, whether to retry transmitting a response signal. In this case, only when a retry determination unit of one of the auxiliary devices determines to retry transmitting the response signal, will that auxiliary device retransmit the response signal in the third time slot subsequent to the third time slit wherein the response signal was first transmitted.
With this configuration, even if two or more auxiliary devices start transmitting their response signals at the same timing, so that the transmissions collide with each other, as soon as one determines to retransmit and the other determines not to retransmit based on the probability, then only one auxiliary device will transmit its response signal at that timing. As a result, a request for response can be properly and quickly transmitted to the main device. One auxiliary device can transmit a response signal in a relatively short time, so that auxiliary device can reliably and even more rapidly start communication.
It is desirable that the wireless transmission system be a cordless transmission system connected to a telephone line. With this configuration, in a cordless telephone system, the main device receives and transmits data to auxiliary devices when, for example, an incoming call is received over the telephone line. Accordingly, the auxiliary devices of the cordless telephone system will not mix signals with devices of other systems, so that connection of incoming telephone calls can be quickly performed.
According to another aspect of the present invention, a wireless transmission system includes a main device, plurality of auxiliary devices, and a timing controller. The main device and the plurality of auxiliary devices communicating data use a multiple access transmission scheme. The main device transmits to the plurality of auxiliary devices over an outgoing frequency of a single wireless channel. The plurality of auxiliary devices transmit to the main device over an incoming frequency of the single wireless channel.
The timing controller controls the main device and the plurality of auxiliary devices to communicate using multiple access based on repeating time-slot cycles. In each time-slot cycle, the timing controller controls the main device to transmit a call signal to the plurality of auxiliary devices in a first time slot; at least one of the plurality of auxiliary devices to transmit in a second time slot a notification signal notifying that the single wireless channel is presently being used; and any of the plurality of auxiliary devices that are in an off-hook condition to transmit in a third time slot an off-hook signal to the main device.
According to another aspect of the present invention, a wireless transmission system includes a main device, a plurality of auxiliary devices, and a multiple access synchronizer. The multiple access synchronizer synchronizes communication of data between the main device and the plurality of auxiliary devices using a multiple access transmission scheme wherein data is exchanged in fixed-width time slots during repeating time-slot cycles. The multiple access synchronizer allots in each time-slot cycle: a first time slot to the main device for transmitting signals to the plurality of auxiliary devices over an outgoing frequency of a single wireless channel; a second time slot to at least one of the plurality of auxiliary devices for transmitting a notification signal notifying that the single wireless channel is presently being used; and a third time slot to the plurality of auxiliary devices for transmitting signals to the main device over an incoming frequency of the single wireless channel.